The present invention relates to control systems for managing electrical power consumption.
The present invention is intended for use in all-electric homes, industrial buildings, and other facilities which are billed by a utility company not only on the basis of total electrical power usage, but on the basis of a peak power usage in a given interval, such as a 15 minute period. In other words, if more than a fixed amount of power, in kilowatts, is used in a 15 minute period, the customer is billed an additional amount. The utility company does this to encourage customers to level out their demand over a 24 hour period to reduce concentrated demands on utility company equipment which can cause black-outs or brown-outs.
A number of prior art devices have been devised to allow customers to level out their power demands.
Lenhart et al., in U.S. Pat. No. 3,862,430, disclose an electrical demand limiting system in which power consumption by a residence or other facility is measured and is compared with a plurality of preselected demand limits, each of which is a percentage of the total permissible power demand. Logic circuitry comprising comparators and flip flops is used to disconnect the various loads.
Deslisle et al., in U.S. Pat. No. 3,714,453, disclose a load regulating system which takes advantage of the thermal inertia of the power company's kvameter to regulate the load closely within power company limits. Certain nonregulated loads can never be dropped. In one mode, loads are dropped and reconnected according to a predetermined, fixed order; in another mode, they are cycled at fixed intervals.
In the device of Spethmann, U.S. Pat. No. 4,147,296, a demand limit controller for reducing a plurality of heating or cooling loads by a proportional amount is disclosed as being amenable to computer control. Each load is controlled through a fluid valve by a resettable temperature controller having inputs from a temperature sensor and a proportional demand controller.
Pollnow in U.S. Pat. No. 4,125,782 discloses a microprocessor-controlled demand controller which determines shed and restore points as a function of the present rate of power consumption. The computer is arranged in a standard form, comprising a CPU, ROM, RAM, and PIA's. A PIA is connected to eight output circuits, each operating a different load. The control panel utilizes thumbwheel switches connected to the unit through input circuits to generate 4 bit BCD digits to the PIA. A priority switch 5 selects a fixed priority mode or a rotating priority mode through a switch circuit. A demand interval is divided into 90 increments and the rate at which power was consumed during the last 9 increments is compared with power consumption over the entire demand interval. If power consumption is rising slowly toward the demand objective, loads are shed at a later time than if power consumption is rising rapidly.
Hall, in U.S. Pat. No. 4,071,745, discloses an electronic system for controlling a measured temperature in a house or other building according to various time intervals. The system utilizes a microcomputer but is not connected to power input. The device saves energy by temperature setback and by reduction of the degree of control of the temperature. Data entry is accomplished by data entry switches, function switches, and mode switches. Temperature is input through a transducer. Preferably, there are 24 possible time intervals. During each interval the temperature measured by the transducer is repeatedly compared with a stored reference temperature to generate appropriate control signals for the cooling and heating systems.